This invention relates to a vibration generator.
Portable devices such as cellular telephones serving as the terminals of a mobile communications system sometimes contain a vibration generator within the portable device itself or within an accessory thereof to inform the user of an incoming call by silent vibration rather than by an audible ringing tone. The vibration produced by the generator is sensed by the human body to alert the user to the call.
Structurally speaking, the conventional vibration generator of this type includes a motor having a rotary shaft and a rotating body mounted on the shaft, wherein the center of gravity of the rotating body is located at a position different from that of the rotary shaft so that vibration is produced when the rotating body is rotated.
In a vibration generator having a structure of this kind, wobbling of the rotary shaft produced when the rotating body is rotated is utilized as the source of vibration. Consequently, the bearings of the rotary shaft of the motor are subjected to excessive force, a situation which detracts from the durability and reliability of the generator.
Taking note of the simple harmonic motion of a movable element that is fixed to the free end (movable end) of a spring, the Applicant has previously proposed a vibration generator (Japanese Patent Application Laid-Open No. 10-180186) which, as shown in FIG. 8, includes a generally C-shaped yoke 210 about which a coil 240 is wound, a leaf spring 220 having a lower end fixed to the approximate center of the yoke 210, and a movable element 230 fixed to the upper, movable end of the leaf spring 220.
The movable element 230 includes two permanent magnets 235, 236 attached to respective ones of both sides of the yoke 234. When a prescribed current is passed through the coil 240, the movable element 230 undergoes simple harmonic motion so that the leaf spring 220 is deflected from side to side.
The proposed vibration generator, however, has a number of shortcomings.
Specifically, though the leaf spring 220 is used as a resilient member for supporting the movable element 230, the leaf spring 220 is highly rigid. As a consequence, there is the danger that the leaf spring 220 will break with prolonged operation. Though the leaf spring 220 may be lengthened in order to prevent this, such an expedient makes it difficult to reduce the size of the vibration generator.
Another problem is that since the leaf spring 220 is fixed to the yoke 210 and movable element 230 by screws or rivets, the fixing operation is troublesome.
In addition, since two permanent magnets 235, 236 are used, this is an obstacle to cost reduction.
Furthermore, the conventional vibration generator does not produce enough vibratory thrust. A vibration generator capable of producing stronger thrust is desired.